Method of drilling wells



METHOD- OF DRILLING WELLS No Drawing. Application July 21, 1936, Serial No. 91,702

18 Claims.

This invention relates to the drilling of wells and more particularly to the control of the heaving shale encountered in the drilling of such wells.

This application is a continuation-in-part of 5 our copending application Serial No. 46,893, filed October 26, 1935.

More specifically, our invention relates to the preparation and use of drilling muds so constituted and controlled in composition that when employed in the drilling of a well traversing or penetrating a heaving shale formation, the heaving of the shale is substantially prevented. According to our invention this may be accom- F plished by the use of sodium silicate in the a drilling mud.

Drilling muds are almost universally used in the drilling of wells employed for tapping underground collections of oil, gas, brines, and water. These muds fulfill various functions, the most 20 important of which are to assist in the removal of cuttings from the wells, to seal formations of gas, oil and water which may be encountered at various levels and to lubricate the drilling tools and the drill pipes which carry the tools.

25 In the course of drilling wells, the bores may encounter certain geological formations which are termed heaving shale formations or more simply heaving shale. The term denotes shalestrata which do not remain consolidated during 30 the drilling operations. In some cases, .the shale heaves or caves into the hole when the drilling tools are removed therefrom and in other cases the shale may heave in the course of the actual drilling. In the latter case, the shale may bind 35 or pinch the drill stem, thereby preventing its rotation or even resulting in its destruction.

Our experience leads us to conclude that there are various types of heaving shales which react difierently; some may be controlled merely by me- 40 chanical methods, whereas others require chemical treatment for successful control. Various theories have been advanced for explaining the heaving of shales which may be controlled by mechanical means. One is that the heaving of 45 shale is caused by pockets of high pressure gases which exist in the crevices and partings of the shale formations. Another theory is that this class of heaving shales is under considerable -u'nrelieved stress and that the drilling of, a'hole through the shale forms an opening into which the shale can slideor cave to partially relieve the inner stress. I

The class of heaving shales which require chemical treatment for successful control apparently disintegrate when they are contacted with aqueous drilling mud and experiments indicate that it is the water content of the drilling mud which brings about this disintegration. Several methods have been proposed for chemically controlling shales of this type. For example, one 5 method involves incorporating in the drillingmud water soluble salts, such as calcium chloride, magnesium chloride or other salts which are naturally found within the shale formations. This method of treatment is based upon the theory that the heaving'or disintegration of the shale is brought about by the osmosis of the water content of the drilling mud to deposits of salts naturally occurring within the shales, the pressure under which this osmosis takes place being sufliciently great to'disintegrate the shale.

We have found that the incorporation of salts having a high osmotic pressure in drilling muds does not prevent the heaving of shale contacted with such drilling muds. We have also found that heaving shales' which disintegrate with great rapidity in water disintegrated as rapidly in aqueous solutions of alkali and alkaline earth' salts. On the basis of this work we have concluded that osmosis is not responsible for the heaving of shale.

According to our invention, shale formations which normally disintegrate upon contact with water, may successfully be penetrated in drilling operations without heaving by employing a. drill- 0- ing mud consisting essentlally'of clay, water and sodium silicate. We have found that not every type of sodium silicate may be employed successfully and that for obtaining beneficial results sodium silicates in which the proportion of NaiO is less than that of the S102, and more particularly sodium silicates with molecular ratios of sodium oxide to silica of..from 1:2 up to 1:39, should be employed. Furthermore, our results indicate that the use of sodium silicate in which 40 the molecular ratio of sodium oxide to silica is about 1:3.4 yieldsdrilling muds which are very satisfactory on heaving shales and we have set forth hereinafter the results obtained with this type of sodium silicate.

Commercial sodium silicates are commonly available in water' solutions of varying viscosity. They are placed on the market in watersolution at concentrations near the practical limit of viscosity for the purpose of avoiding the expense, of 5; shipping unnecessary amounts of water. It is well known that these commercial sodium silicate solutions range in water content from about 45% to about 70% for the sodium silicates having a molecular ratio of sodium oxide to silica of from 1:2 up to 1:3.9. We appreciate that commercial sodium silicate solutions are prepared by dissolving in water solid sodium silicates which are sometimes spoken of in the art as sodium silicate glass. In the practice of our invention we contemplate the use of commercial sodium silicate solutions without regard to their method of preparation. In the use of the term sodium silicate throughout the specification and claims, We refer to these commercially available sodium silicate solutions, having the above indicated water contents.

The method which we have discovered of preventing the heaving of shale is in nowise similar to those methods which involve treating rock formations with sodium silicate or other salts to react with Water soluble precipitants such as high valency metal salts or acids whereby water insoluble precipitates are formed. On the contrary, the success of our process is not dependent upon the precipitation of water insoluble silicates by reaction of the sodium silicate content of our mud with water soluble precipitating salts or acids. In fact, we have .found that our process is entirely effective in preventing the heaving of shale which contains substantially no calcium or magnesium or other water soluble precipitating salts or compounds.

To explain the extraordinary results obtained with our drilling muds, we advance the following theoretical explanation to the correctness of which, however, we do not intend to limit ourselves.

The heaving shalcs which disintegrate in the presence of water apparently display a butter action in that they tend tq maintain the pH value of aqueous media in which they are placed at a pH value of from 7 to 9. The sodium silicate drilling muds which we employ have pH values in the neighborhood of 11.00 and, therefore, when the drilling mud comes in contact with the heaving shale, the tendency of the latter, due to its buffering characteristics, is to reduce the pH of the drilling mud with the result that a precipitation of silica gel occurs. Since this reaction is apparently of low velocity, the aqueous solution of. sodium silicate constituting the liquid phase of the drilling mud has an opportunity to penetrate into the shale particles. This may explain why particles of heaving shale which have been subjected to our treatment are not superficially coated but are in fact impregnated with a cementing material which we believe tobe silica gel.

We are cognizant of the fact that the use of sodium silicate in drilling muds has been pro posed for maintaining drilling muds in the proper state of colloidal dispersion. In these cases, the sodium silicate is employed to bring about the precipitation of calcium and magnesium ions which apparently have been recognized as having a deleterious effect upon drilling muds. In using sodium silicate for this purpose, only sufllcient is used to bring about the precipitation of the calcium and magnesium ions present; usually a quantity in the neighborhood of several tenths of one percent is adequate. On the contrary, we contemplate the use of much greater proportions of sodium silicate than are necessary for precipitating calcium and magnesium ions.

Our invention may be applied in numerous ways. For example, the preferred type of sodium silicate may be added to a previously prepared drilling mud, or else a drilling mud may be formed by incorporating clay or other finely- .divided materials in a solution of sodium silicate.

We do not intend to limit ourselves to any particular method of compounding or preparing the drilling muds employed by us in efl'ecting the operation of our invention.

As a typical example of the application of our invention, we give herewith a description 01. a drilling mud which was employed for successfully drilling a well into and through heaving shale located on the Bryan Mound at Freeport, Texas. A drilling mud consisting essentially of clay and water was prepared and so compounded that its weight was approximately 9.3 pounds per gallon. This mud had a viscosity of 6 centipoises. There was then added thereto sufficient sodium silicate to yield a mud which contained 33% by volume of the sodium silicate. The sodium silicate used was one in which the molecular ratio of NazO to $102 was approximately 1:3.4. It had a water content of approximately 62%. An examination showed that the mud had been increased in weight to 9.9 pounds per gallon and that the viscosity had been raised to 37 centipoises. This mud was used in the usual manner, being continuously circulated through the drill pipe to the locus of drilling where it picked up cuttings and drilling debris and carried them suspended therein, upwardly to the surface where the cuttings-laden mud was passed into the settling pit and the cuttings allowed to settle out. The mud was then recirculated to the drill pipe and thence downwardly to the locus of drilling. While the mud was in use, there was added thereto from time to time a solution of the same type of sodium silicate in the proportion of 33% by volume of the commercial form dissolved in 67% of water in order to make up for loss. It was apparent that very little of "the shale disintegrated since there was no appreciable increase in the amount of suspended finely-divided solids present in the mud.

Although we employed 33% by volume of the 1 to 3.4 ratio sodium silicate in the above mentioned drilling operation, we contemplate the use of lower and higher percentages, preferably from 20% to 70% by volume. Although we have shown the use of a sodium silicate in which the molecular ratio of sodium oxide to silica is about 1 to 3.4, it may be found desirable to employ sodium silicates of difierent molecular ratios. In those cases we contemplate the use of sodium silicates in which the molecular ratio of sodium oxide to silica falls within the range of from 1 to 2.0 up to 1 to 3.9.

We recognize that sodium silicate is also avail able in ratios of sodium oxide to silica ranging from 1:2 down to 1:1 (sodium metasilicate) and that these sodium silicates partake of the properties of the silicate of 1:2 ratio in varying degrees. Some ofthese sodium silicates may be effective in practicing our invention when encountering certain shales, but for general use we prefer to use sodium silicates within the range of ratios of sodium oxide to silica of 1:2 up to 1:3.9.

It is to be understood that our invention is not to be confined only to drilling muds containing clay, but to drilling muds containing other finelydivided solids, such as iron oxide, barytes, bentonite, and in fact any of the finely-divided materials, which, upon dispersion in water, yield satisfactory drilling fluids.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof and only such limitations should arouses be imposed as are indicated in the appended claims.

We claim:

1. A drilling mud useful for preventing the heaving of shale comprising a finely divided solid, water and 20% or more by volume of a sodium silicate in which the molecular ratio of sodium oxide to silica falls within the range of from 1:2 up to 123.9.

2. A drilling mud useful for preventing the heaving of shale comprising clay, water and 20% or more by volume of a sodium silicate in which the molecular ratio of sodium oxide to silica falls within the range of from 1:2 up to 113.0.

3. A drilling mud useful for preventing the heaving of shale comprising clay, water and from 20% to by volume of a sodium silicate in which the molecular ratio of sodium oxide to silica falls within the range of from 1:2 up to 1:3.9.

4. A drilling mud useful for preventing the heaving of shale comprising a finely divided solid, water and fmm.20% to 70% by volume of a so dium silicate in which the molecularratio of sodium orgide to silica falls within the range of from 1:2upto 1:3.9.

5. A drilling mud useful for preventing the' heaving of shale comprising a finely divided solid, water and from 20% to 70% by volume of a sodium silicate in which the molecular ratio of sodium oxide to silica is about 1 to 3.4.

6. A drilling mud useful for preventing the heaving of shale comprising a clay, water and from 20% to 70% by volume of a sodium silicate in which the molecular ratio of sodium oxide to silica is about 1 to 3.4.

7. In the drilling of wells with the use of a drilling mud, the method of preventing the heaving of shale encountered in the well, which comprises circulating through the well a. drilling mud comprising a finey divided solid, water and 20% or more by volume of a sodium silicate in which the molecular ratio of sodium oxide to silica falls within the range of from 1:2 up to 1:3.9.

8. In the drilling of wells with the use oi a drilling mud, the method of preventing the heaving of shale encountered in the well, which comprises circulating through the well a drilling mud comprising clay, water and 20% or more by volume of a sodium silicate in which the molecular ratio of sodium oxide to silica falls Within the range of from 1:2 up to 123.0.

9. In the drilling of wells with the use of a drilling mud, the method of preventing the heaving of shale encountered in the well, which com prises circulating'through the well a drilling mud comprising a finely divided solid. water and irom 20% to 70% by volume of a sodium silicate in which the molecular ratio of sodium oxide to silica falls Within the range of from 1:2 up to 1:3.0.

10. In the drillingof wells with the use of a drilling mud, the method of preventing the heaving of shale encountered in the well, which comprises circulating through the well a drilling mud comprising clay, water and from 20% to-70% by volume of a sodium silicate in which the molecular ratio of sodium oxide to silica falls Within the'range of from 122 up to 1:3.9.

11. In the drilling of wells with the use of a drilling mud, the method of preventing the heaving of shale encountered in the well, which comprises circulating through the well a drilling mud comprising a finely divided solid, water and from 20% to 70% by volume of a sodium silicate in which the molecular ratio of sodium oxide to silica is about 1:3.4.

12. In the drilling of wells with-the use of a drilling mud, the method of preventing the heaving of shale encountered in the well, which comprises circulating through the well a drilling mud comprising clay, water and from 20% to 70% by volume of a sodium silicate in which the molecular ratio of sodium oxide to silica is about 1:3.4.

13. A drilling mud for preventing heaving of shale comprising a finely divided solid, water and sodium silicate in which the molecular ratio of silica to sodium oxide is about 2, and the weight of the sodium silicate used is about one quarter oi the weight of the total mud.

14. A drilling mud comprising sodium silicate in aqueous dispersion in an amount and of a character effective to prevent the heaving of shale.

15. A drilling mud comprising water glass in an amount and of a character efiective to prevent the heaving of shale.

.16. In the drilling of wells with the use of a drilling mud, the method which comprises circulating through the well a mud comprising sodium silicate in aqueous dispersion in an amount and of a character effective to prevent the heaving of shale.

17. In the drillingof Wells with the use of a drilling mud, the method which comprises circulating through the well a mud comprising water glass in an amount and'of a character effective to prevent the heaving of shale.

18. A drilling mud according to claim 14 containing bentonite dispersed in water. 

